Render always displaying as completely white?
You are looking at the Depth pass
I think you are just looking the wrong render pass (or at least, not the one you were expecting to see).
In the image editor menu's tab there's a field where you can control which one of the render passes you set up for the render layer should be shown.
The Combined pass it's probably what you are expecting to see, but currently you set the filed to Depth.

You just have to switch it back as shown in the image sequence above.
If you are wandering why the Depth pass (also called z-pass, or z depth pass....) is all white, I'll suggest to read this related question:
Z depth pass in Cycles, rendering white